1. Field of the Invention:
The present invention is directed to novel isocyanate terminated prepolymers of carboxylic acid grafted polyethers, salts of these prepolymers and polymers derived therefrom. More specifically, the present invention relates to reacting an ethylenically unsaturated mono-carboxylic acid with a polyether in the presence of a free radical initiator to form a graft copolymer. Acid-containing isocyanate terminated prepolymers can thereafter be formed by reacting the graft copolymer with a polyisocyanate. Alternatively, salt-containing isocyanate terminated prepolymers can thereafter be formed by reacting the acid-containing prepolymer with a base. Finally, either the acid containing or salt containing isocyanate terminated prepolymer can be cured with an isocyanate reactive material to form a polymer.
2. Prior Art
Reactions of organic acids with polyols are well known. The best known reaction between these compounds is the formation of polyester polyols where the acid group of an organic di acid reacts with the hydroxyl group of a diol forming an ester linkage and eliminating water. Using a stoichiometric excess of hydroxyl groups the product can be hydroxyl terminated. This type of product is useful in the preparation of polyester based polyurethanes.
Technigues for producing copolymers by graft polymerizing ethylenically unsaturated monomers onto polymer backbones are, in general, well known. However, the resultant graft copolymers are often seriously contaminated with unwanted by-products resulting from side reactions, one common contaminant being homopolymers of the monomer used during the graft polymerization. An example of this can be found in U.S. Pat. No. 4,250,077. This patent teaches mixing olefinically unsaturated carboxylic acids with many types of polyols and polymerizing the mixture with free radical catalyst to produce a graft copolymer. The preferred acid is acrylic acid which polymerizes with itself. However, additional unsaturated monomers are preferably added to minimize the homopolymerization problem and improve the compatibility of the graft copolymer.
U.S. Pat. No. 4,460,738 teaches a protocol to overcome the problems associated with homopolymerization taught in U.S. Pat. No. 4,250,077 by grafting single di-carboxylic acid units at intervals onto the backbone of an oxyalkylene adduct. The acids are maleic, fumaric and itaconic and the initiators are of the peroxy type. These acids are specifically selected because they do not homopolymerize. However, these di-acids may readily undergo well.known undesired reactions such as dehydration thereby forming the five membered ring anhydride which can subseguently re-open in the presence of a hydroxyl compound. This leads to ester and half acid formation and causes unwanted viscosity build and loss of acid functionality thereby decreasing utility of the resultant polymer. These problems were recognized in this patent and they teach fumaric acid is preferred over maleic acid because "fumaric acid did not dissolve before reacting" resulting in reduced ester formation although they still tend to be generally dark in color and contain significant amounts of ester.
Surprisingly it has been found that isocyanate-terminated prepolymers of mono carboxylic acid grafted polyethers, salts of these prepolymers and fully reacted polymers formed from the salts offer advantages as evidenced by better product color, stability, viscosity, improved clarity and other processing advantages.
It will become evident from the detailed description that prior to the present invention there has been no disclosure of the use of mono carboxylic acid grafted polyethers in such systems. As previously stated, U.S. Pat. No. 4,460,738 teaches the use of di carboxylic acid grafted polyethers and states that "not all carboxylic acids or free radical initiators may be used for this reaction". It has now been found the mono-carboxylic acid grafted polyethers of this invention offer advantages over the materials described in the art including such features as stability and performance.